Transistorized magneto ignition systems are known, and reference is made to U.S. Pat. Nos. 3,864,622 and 3,894,525, both Haubner, Hofer and Schmaldienst, and assigned to the assignee of the present applications. In these ignition systems, an ignition transistor is controlled to become conductive upon start of a positive voltage half-wave derived from the magneto; at the ignition instant, the primary current through the ignition transistor is abruptly interrupted, causing the ignition pulse. The negative voltage half-waves derived from the magneto generator have to be damped within the primary circuit so that the ignition transistor, and other circuit elements, such as control circuits for the ignition system, are not damaged by excessive reverse voltages, loading the ignition transistor, and the other components, in their inverse or blocking direction. Short-circuiting of the negative voltage half-waves by providing a simple diode in parallel to the magneto generator is not suitable since the short-circuit current of the negative half-waves causes a time shift, due to armature reaction, of the positive half-wave necessary for ignition, which results in undesirable retardation of the ignition instant. The aforementioned referenced U.S. Pat. No. 3,864,622, Haubner et al., thus utilizes a damping element connected in parallel to the magneto generator which consists of a diode and a serially connected Zener diode in order to limit the negative half-waves in the primary current to the response level of the Zener diode. The referenced U.S. Pat. No. 3,894,525, Haubner et al., approaches the solution to the problem in a somewhat different way and damping of the negative half-waves is effected by an ohmic resistor, rather than using a Zener diode, and connected in the primary circuit of the magneto generator.
Both solutions in accordance with the prior art have the advantage that the negative half-waves in the primary circuit are damped while a high amplitude of the primary current at the ignition instant, and thus high secondary flash-over voltage pulses can be obtained, whereas retardation of the spark after the top dead center (TDC) position is limited to about zero degree. Both solutions, however, require additional circuit networks for damping of the negative half-waves and thus require additional costs in manufacture as well as in circuit components.